The present invention is directed to videoconferencing and in particular to the way in which a multipoint videoconference is initiated.
Considerable effort has been directed to minimizing the extra capabilities that videoconferencing terminal equipment must be provided. This can be appreciated by considering Recommendation H.323 of the International Telecommunication Union's Telecommunication Standardization Sector.
That recommendation sets forth a standard entitled "Visual Telephone Systems and Equipment for Local Area Networks Which Provide a Non-Guaranteed Quality of Service." Among the methods that it describes are ways to initiate, conduct, and terminate multipoint videoconferences.
The system that H.323 describes for implementing its approach includes terminal, or "endpoint" equipment, such as an appropriately programmed personal computer configured as a network node. Most systems for implementing the H.323 approach also include a gatekeeper. A gatekeeper manages the videoconferencing activities of various endpoints and other equipment within a "zone" of such equipment that has registered with the gatekeeper in accordance with procedures that H.323 sets forth. The gatekeeper's responsibilities vary from implementation to implementation, but they typically include granting videoconference access to the network on the basis of whatever policies the administrator has imposed, allocating network bandwidth among videoconferences, and providing address translation.
Giving the gatekeeper the address-translation task is one way in which system designers minimize endpoint-capability requirements: they thereby relieve the endpoints of the need to keep track of various potential participants' network addresses. To designate a called party, for example, a user may enter an easily remembered alias such as "doe.john@marketing.erie." For actual signal transmission to the other party, though, that alias must be translated into a network address such as "170.242.67.3." Rather than maintaining a translation table, which would ordinarily require frequent updating, the endpoint simply sends a message to the gatekeeper asking for address resolution.
Some capability-minimization efforts are directed particularly to multipoint conferences, i.e., conferences having more than two participants. For a multipoint conference, H.323 requires a "multipoint controller," which coordinates the conference by performing tasks such as mediating the negotiation of communications modes, determining which participants will receive which other participants' outputs, etc. Although H.323 admits of arrangements in which every endpoint's terminal equipment implements a multipoint controller, such an approach tends to be demanding of terminal-equipment resources and is inconvenient from a maintenance standpoint. So systems administrators tend to provide one or more shared multipoint control units that implement the necessary multipoint controllers and to provide multipoint coordination through communications between those units and endpoints not so provisioned.
Another reduction in endpoint-capability requirements results from the way in which the conference's video, audio, and data signals are distributed. When the multipoint controller directs that, say, participant A's output signals are to go to participants B and C, participant A may multicast (or separately unicast) its outputs directly to the other participants. Also, participant A may receive the other participants' signals, and his system may so mix those signals as to enable him to view both other participants simultaneously on his monitor. But this presupposes that participant A's endpoint equipment can keep track of the other participants and perform the necessary multicasting and mixing. Again, requiring all terminal equipment to have such a capability is a heavy resource burden.
So system designers have instead provided the shared multipoint control units with multipoint processors. A multipoint processor acts as an intermediary, distributing each participant's signals to each other participant that is to receive them. Instead of sending its signals to each such other participant, each participant communicates only with the multipoint control unit: from the endpoint terminal's viewpoint, the video, audio, and data transmission are the same as in a two-party video call.
Typically, some external mechanism is used to cause the multipoint control unit to schedule a conference, for which that unit allocates a conference name. At the appointed time, the multipoint control unit calls the participants, or one or more of them call it with a message that includes the conference name, and the conference proceeds for each endpoint as though it were simply a point-to-point call with the multipoint controller. (The conference name is a normal part of point-to-point calls, too.)
Still, if one or both of a point-to-point call's terminal equipment additionally includes a multipoint controller, H.323 provides for expanding a point-to-point conference on an ad hoc basis to a multipoint conference. Presumably, the endpoint process would be arranged to include a capability for communicating conference-invitation requests to the multipoint-controller process, which would then call each new participant.